Fluorescent lamps have been widely used in many residential, commercial and industrial lighting applications as they offer high efficacy (lumen per Watt) and have proven operational stability. As they require a high ignition voltage to discharge the lamp and have negative resistance, a device called a ballast is used to generate the ignition voltage and regulate the lamp current.
Ballasts are of two major kinds: a low-frequency electromagnetic type and a high-frequency electronic type. Electromagnetic ballasts are made of passive components. They have the advantages of high reliability, long lifetime, and robustness against transient voltage surge and a hostile working environment. However, their energy efficiency, input power factor and power density are typically low. Electronic ballasts are now widely adopted as they have an overall economic benefit compared to other solutions. Moreover, they have good performance characteristics such as high input power factor, low input current harmonics, good lamp current crest factor, and low flickering. Operating the lamps at high frequency can also attain a higher efficacy than mains-frequency-operated electromagnetic ballasts.
With recent advancements in microelectronics technology, light-emitting-diode (LED) lighting is now becoming increasingly popular for general lighting and special purpose lighting applications. Compared with fluorescent lamps, LEDs have longer life expectancy and higher resistant to vibration failure. They also consume considerably less power. Moreover, they can operate on a low voltage. Thus, it would be advantageous if fluorescent lamps could be substituted by LED lamps in existing installed lamp fittings. This would enable the existing lamp infrastructure to be retained which is clearly desirable. However, even though the existing fluorescent lamp fixtures/fittings could be retained, the ballasts (electromagnetic or electronic) installed inside such lamp fixtures would have to be removed or replaced by LED drivers. This requires rewiring of the lighting circuits which is time consuming and expensive, particularly as it has to be performed in situ with the existing fittings and fixtures.